2 GPS antenna under cowling?

[RV8JD]

Garmin antenna mounted on the turtledeck of my previous RV-8:

[zippymp8]

I have a shelf in front of the firewall with two GPS antennas (G3X touch & GTX335 with gps) in close proximity. Just my data point so far, but I have not seen any negative issues yet, passed the ADS-B test, seeing a display of 7ft accuracy in flight. (early days still).

[Carl Froehlich]

Originally Posted by RV8JD

Garmin antenna mounted on the turtledeck of my previous RV-8:

Did the same for the GTN-650 antenna on the RV-8A and RV-8. The SkyView GPS antenna is happy on top of the glare shield - covered with a piece of dark cloth to prevent glare on the canopy.

Carl

[BillL]

I have a 7 with two GPS antenna mounted under the cowling. The temps measured in operation show under the recommended limit, and they are high enough for minimum shading from the rear but better view forward and to the side. 250 hrs. No dropouts ever, but have not flown everywhere.

One issue though - I failed the 35 on an IFR plan - thankfully near the airport and VFR at the time. It failed and blocked all the other GPS under the cowl as they were too close together. A failure mode unaccounted for in the locations. Next time the 650 breaker will get pulled.

Although I reinstalled in the same location, if the time clock were rewound - it would go aft of the cockpit where a failure would not have overpowered and jammed the other GPS antenna.

[Tankerpilot75]

The builder of my RV7A mounted the two non-WAAS gps antennas on separate mounting brackets under the cowl about 3-4” forward of the firewall. Two years ago I mounted a WAAS antenna between the two other gps antennas for my Garmin 335 adsb with internal gps. The airplane now has over 540 hours on it and the two nonWAAS gps antennas are still working and my WAAS gps antenna has over 100 hours without problems.

However, if I was to do it again I would not place them where they’re at. The environment gets really hot and like others have said electronics don’t like heat. Frankly I recommend placement on top of the aircraft behind the cargo panel where you can easily use doublers and get access if needed. Remember, putting ascetics above functionality and reliability is always a poor trade off.

[JDeanda]

I was chary about putting a GPS antenna under the cowl. Nice to get it far forward in our tailheavy RV-6. Not too hard to keep it cool enough… until you park the airplane. So I mounted mine on a simple bent aluminum bracket on the fore and aft bit right behind the roll bar, under the canopy. Works great and I hope its a reasonable compromise for Wt. & Bal. considerations. At least its really light. I’ve had a Wild Thought about mounting it under the forward deck, between the firewall and the structural bulkhead forward of the instrument panel. I’d have to cut a fairly generous sized hole, maybe a round 6” diameter one, in the skin to add a fiberglass radome, and I suppose that radome would need to be fairly thick to handle the structural load of the missing aluminum. And of course it would beed to be removable from outside the airplane because I’m getting old and crotchety about going under the panel these days. Yeah, a lot of work for not much gain. But kinda cool, maybe?

[vomatic]

How are you guys routing your coax to rear your mounted GPS antenna? Are you taking it down the top side rails or under the floor? Are you going up the rear seat bulkhead through the baggage compartment or taking it all the way back the the last baggage compartment bulkhead, up the back side and then forward on the top of the baggage compartment? Any pics???

My plan is to go under the floor and up the rear seat bulkheads. Unless someone has a better idea.

Thanks guys.

[laserman]

All three GPS antenna's -- work great here...

Right over the panel... Easy wiring !!

Painted them too.. No Problem. (Walmart.. Flat black paint).. yes did testing to show no. issues with painting

Note location of temp sensor..

See log link below for more details


Al

[Bavafa]

You may get the report of worked fine from many but it really depends on what is meant by 'fine'

On my last build, I put my G3X antenna under the cowl, maybe a couple of inches from the FW and I do pick up satellites and position without any issues but upon investigating a different issue, I was told by Garmin that my GPS data is not as reliable as it needs to be and since the AHAR drives some of its calculation based on GPS position, I was advised to look into it.

I installed the antenna on the glareshield and the data was clean and as reliable as it can be expected.
Also be mindful that for WAAS antenna, there is a minimum and maximum cable run, at least for Garmin, so you may end up with a coil of coax under the penal.

[Carl Froehlich]

Originally Posted by vomatic

How are you guys routing your coax to rear your mounted GPS antenna? Are you taking it down the top side rails or under the floor? Are you going up the rear seat bulkhead through the baggage compartment or taking it all the way back the the last baggage compartment bulkhead, up the back side and then forward on the top of the baggage compartment? Any pics???

My plan is to go under the floor and up the rear seat bulkheads. Unless someone has a better idea.

Thanks guys.

The RV-8 design provides for a wire run on both port and starboard sides under the canopy rail. Look at the holes at the top of the side ribs - these accept snap bushings.

On the current RV-8 I used these holes for:
- Static tubing to the panel (feeds the panel mounted analog airspeed instrument)
- SkyView network cable
- GTN-650 GPS antenna coax
- Wire to connect wing mounted OAT sensors to the ADHARS modules
- ELT power, GPS position serial, and ELT “phone” control cable

Under floor cables include:
- Power from the rear mounted PC-625 battery and associated control wiring. Forward PC-625 is mounted in the forward baggage well.
- ADS-B receiver (single four #22 conductor shielded wire)
- Autopilot pitch servo cable
- Tail NAV/Strobe cable
- AOA and Pitot tubes

Carl